Despite recent evidence of anatomical specificity, behavioral studies have generally concluded that cells in the medial ponto-medullary reticular formation (RF) have relatively nonspecific roles in either attention, sleep, motivation, regulation of muscle tone or in other activities. Using techniques that this laboratory has developed for behavioral analysis and unit recording in freely moving animals, a number of RF cell types have been discovered. Each cell type has a specific motor correlate and a unique pattern of sensory and reflex response, sleep cycle discharge and anatomical distribution. On the basis of these studies and recent anatomical and neurophysiological data, we have hypothesized that most RF cells generate specific patterns of muscle contraction in the axial musculature. We propose to use spike triggered averaging to analyze the contribution of RF head movement cells to excitation and inhibition in neck flexors. We will determine whether the activity of these cells precedes or follows activity in the contracting muscles. Using antidromic and orthodromic stimulation from spinal cord, motor cortex, tectum and vestibular nucleus, the differences in synaptic inputs and axonal outputs of behaviorally defined cell types will be determined. This analysis will allow us to link behavioral cell type identification with the large body of physiological and anatomical data identifying RF cells on the basis of monosynaptic inputs and axonal outputs. Recent reports finding no motor, postural, or other behavioral deficits after kainic acid lesions of the RF pose a major problem for the specific motor hypothesis of RF function, and other RF hypotheses. We propose to identify behavioral deficits after ibotenic acid lesions of the RF by the use of more sensitive measures of motor activity. Pilot studies for this experiment have provided the first evidence of motor deficits after axon sparing lesions of the RF. The relative contributions of cell bodies and axons to lesion effects will be assessed by using lidocaine injections to reversibly block fibers of passage. The acute behavioral effects of neuronal stimulation after injection of ibotenic acid will also be determined. These studies should permit the anatomical localization of behavioral functions within the RF and the identification of the cellular elements participating in these functions. Changes in normal RF operation are likely to contribute to a number of sleep and motor disorders.